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# Magnesium Sulphate ## Overview Magnesium sulphate is an electrolyte that plays a crucial role in numerous biochemical processes. It is available for intravenous (IV) and intramuscular (IM) administration. ## Primary Indications * Treatment of hypomagnesemia. * Management of pre-eclampsia and eclampsia. * Treatment of status epilepticus (adjunctive therapy). * Management of Torsades de Pointes. * Bronchodilator in severe asthma exacerbations. ## Adult Dosing * **Hypomagnesemia:** * Severe symptomatic hypomagnesemia: 4 to 6 grams IV as a loading dose over 5-15 minutes, followed by 1 to 2 grams per hour as a continuous infusion. * Less severe hypomagnesemia: 1 to 2 grams IM divided into 4 doses over several hours, or 1 to 2 grams IV over 1-5 minutes. * Maintenance: 1 to 2 grams IV or IM every 4-6 hours as needed. * **Pre-eclampsia/Eclampsia:** * Loading dose: 4 to 6 grams IV infused over 5-20 minutes. * Maintenance infusion: 1 to 2 grams per hour. May be adjusted based on clinical response and serum magnesium levels. * IM administration (alternative): 5 grams IM in each buttock initially, followed by 5 grams IM every 4 hours. * **Torsades de Pointes:** 1 to 2 grams IV in 10-50 mL D5W over 5-10 minutes. May repeat if necessary, followed by an infusion of 0.5-1 gram per hour. * **Status Epilepticus (Adjunctive):** 1 to 2 grams IV over 5-15 minutes. * **Asthma Exacerbation (Severe):** 1.2 to 2 grams IV infused over 15-30 minutes. *Specific dosing, particularly for eclampsia and pre-eclampsia, may vary based on institutional protocols.* ## Pediatric Dosing Dosing in children is highly variable and depends on the indication and weight. Consultation with a pediatric specialist or pharmacist is recommended. * **Hypomagnesemia:** * IV: 25-50 mg/kg per dose (equivalent to 0.1-0.2 mmol/kg) infused over 1-4 hours. Maximum dose 2 grams. * IM: 25-50 mg/kg per dose (equivalent to 0.1-0.2 mmol/kg) divided into 4 doses over 24 hours. Maximum dose 2 grams. * **Eclampsia (Adjunctive):** Similar to adult dosing, adjusted for weight. 40-50 mg/kg IV loading dose over 10-20 minutes, followed by maintenance infusion. * **Asthma Exacerbation (Severe):** 25-75 mg/kg IV infused over 15-30 minutes. Maximum dose 2 grams. *Pediatric dosing requires careful calculation and monitoring due to the potential for toxicity.* ## Dose Adjustments * **Renal Impairment:** Magnesium sulphate is renally excreted. In patients with renal insufficiency, doses should be reduced and serum magnesium levels closely monitored to prevent accumulation and toxicity. ## Contraindications * Hypermagnesemia. * Heart block (greater than first degree) without a cardiac pacemaker. * Myocardial infarction. * Potentially in patients with severe renal impairment where accumulation is a significant risk. * Hypocalcemia. ## Adverse Effects * **Common:** Flushing, diaphoresis, hypotension, nausea, vomiting, drowsiness, decreased reflexes. * **Serious:** Respiratory depression, cardiac arrhythmias, cardiac arrest, hypocalcemia, loss of deep tendon reflexes, muscle weakness, confusion, coma. ## Key Drug Interactions * **Neuromuscular Blocking Agents:** Magnesium can potentiate neuromuscular blockade, increasing the risk of prolonged respiratory paralysis. * **Calcium Channel Blockers:** Additive hypotensive effects and increased risk of cardiac depression. * **Antibiotics (Tetracyclines, Quinolones):** Magnesium can decrease the absorption of orally administered tetracyclines and fluoroquinolones; administer these agents at least 2 hours before or 4-6 hours after magnesium sulphate. * **Digoxin:** May exacerbate digoxin toxicity if hypomagnesemia is corrected rapidly. * **Nifedipine:** Risk of profound hypotension and muscle weakness when used concurrently for pre-term labor (though this use is less common now). ## Monitoring * **Serum Magnesium Levels:** Essential, especially in patients with renal impairment or receiving continuous infusions. Therapeutic levels typically range from 2.0 to 3.5 mmol/L (4.0 to 7.0 mEq/L) for hypomagnesemia treatment. Toxicity is more likely with levels above 4.0 mmol/L (8.0 mEq/L). * **Deep Tendon Reflexes:** Loss of reflexes is an early sign of toxicity. * **Respiratory Rate and Depth:** Monitor for signs of respiratory depression. * **Blood Pressure and Heart Rate:** Monitor for hypotension and arrhythmias. * **Urine Output:** Adequate renal function is crucial for excretion. * **Electrocardiogram (ECG):** May be indicated to monitor for cardiac effects. ## Clinical Pearls * Magnesium sulphate is a potent medication; slow IV infusion is critical to avoid adverse effects like hypotension and flushing. * Always have calcium gluconate readily available as an antidote for severe magnesium toxicity. * In pre-eclampsia/eclampsia, continuous monitoring is vital. Discontinue magnesium if respiratory rate falls below 12 breaths/min, urine output is less than 25 mL/hour, or deep tendon reflexes are absent. * IV administration is preferred for rapid correction of severe hypomagnesemia or for acute conditions like Torsades de Pointes. IM administration is painful and requires deep injection. *** *This information is intended for healthcare professionals. Always consult the most current prescribing information and institutional protocols before administering any medication.*